Integral evaporator and accumulator and method of operating the same



March 25, 1958 A. DUNKELMAN 2,827,774 INTEGRAL EvAPoRAToR AND ACCUMULATOR AND METHOD OF OPERATING THE SAME Filed MaICh lO. 1955 4 Sheets-Sheet 2 BY M /J/I y WW ATTORNEYS.

March 25, 1958 A. DUNKELMAN 2,827,774

INTEGRAL EvAPoRAToR AND ACCUMULATOR AND METHOD OF OPERATING THE SAME Filed March 1o, 1955 4 sheets-sheet s on lov L \J b.

w INVENTOR.

A RNOLD DUNKELMAN.

AUoRNEYs.

March 25, 1958 A DUNKELMAN 2,827,774

INTEGRAL EVAPORATOR AND ACCUMULATOR AND METHOD 0F OPERATING THE SAME Filed March 10, v1955 4 Sheets-Sheet 4 11T] j mm.

ARNOLDv DUNKELMA/v. BY l af/M @t/d4 www 7&4. ATToR/ygys.

aan

NTEGRAL EVAPRATR AND ACCUMULA- TGR AND METHOD F OPERATING THE SAB/iE rnold Eunkelman, Cincinnati, Gillo, assignor to Aveo Manufacturing Corporation, Cincinnati, h10, a corporation of Delaware Application lfdarclx 10, 1955, Serial No. 493,414

Claims. (Cl. 62-126) This invention rela-tes to a novel evaporator particularly adapted for use in a domestic refrigerator or home freezer and to a method for operating the evaporator. The principles underlying the invention can be applied equally well, however, in commercial installations or wherever refrigerant is circulated in a closed system, such as a capillary controlled system, and vaporized in an evaporator to produce a cooling effect.

An important feature of the invention is that it provides more eectivery and economically the accumulator which is conventionally used in conjunction with an evaporator. The accumulator is formed as an integral part of the refrigerant ow channel of the evaporator and, during periods of high demand, increases the heat absorbing capacity of the evaporator.

Another important feature of the invention is the novel method by which the evaporator set forth may be-operated to absorb heat effectively over its entire surface area under all operating conditions with a refrigerating eihciency proportional to the demand imposed on the evaporator by ambient conditions affecting the refrigerator in which the evaporator is used.

ln a conventional evaporator, formed from sheet metal stampings which are brazed together, the accumulator comprises an enlargement of a refrigerant ow pass of such size as to be able to store a sizable volume of liquid refrigerant so that variation in amount of charge can be tolerated. Although formation of such an accumulator constitutes no great problem when such a method of fabrication is employed, the accumulator does not increase the heat absorbing capacity of the evaporator significantly.

Another common fabricating method used for making evaporators-involves the brazing of a sinuous length of tubing to a sheet of metal which is subsequently bent into the form of the finished evaporator. This is known as a tubeon-sheet type evaporator. With evaporators of this type, a spun cylindrical accumulator is normally used. The accumulator is joined to the end of the refrigerant tubing and secured in some suitable manner to the basic sheet of the evaporator to which the tube is attached. Here,the accumulator represents an additional item of cost-and, again, does not improve heat absorbing capacity to any marked degree. v

Recently another method of producing evaporators termed roll bonding has become popular. In this method, a sheet of metal, `such as aluminum, is thoroughly cleaned and, using the silk screen process and a stop-weld material, the pattern of refrigerant ow channels is marked on the sheet. Thereafter another sheet of aluminum is placed against the patterned side of the rst sheet, and these sheets are spot welded to hold them together. The joined sheets are then heated and passed through a rolling mill which elongates the sheets and reduces their combined thickness. Simultaneously, the sheets are homogeneously bonded over all areas not covered by the stopweld pattern. Thereafter, a connection is made at the edge of the sheet with the convolution pattern and uid under pressure is applied to intlate the sheets over the areas ricc between parallel hat platens which limit the extension of the metal in forming iiow passes eventually used for conveying refrigerant. After inflation, the formed plates are bent into an evaporator.

In this type of process, which is desirable from an initial cost and simplicity standpoint, it is dicult, if not impossible, to form a large cylindrical accumulator integrally as in evaporators made from stampings The reason is that it is not possible to stretch the metal during the ination process to any great extent lest rupture occur. As a result, in roll bonded evaporators, the accumulator is normally formed as a relatively fiat volume of quite small thickness. At intervals throughout the volume, localized areas of the opposed Walls are joined for strength purposes. The resulting accumulator covers aconsiderable larea of the finished evaporator and may create a dead'spot which is objectionable under some operating conditions in failing to absorb heat. posed, the volume of the accumulator is quite small, which is objectionable for reasons which will appear later.

The present invention eliminates these problems and teaches an improved way to provide an accumulator in a roll bonded evaporator. Although particularly'useful in this connection, it should be understood, however, that the principles involved may also be used in connection with evaporators made by other processes, as with ltube-onsheet evaporators or in evaporators formed from stampings. The principles may also be employed in connection with methods wherein sheets of metal, maintained at v brazing temperatures, are pneumatically expanded -between dies having the desired contour of the refrigerant ow channels.

Briefly stated, the invention comprises a particular arrangement and volume relationship of continuous refrigerant ilow passages in an evaporator whereby a certain portion of the passages serve as an accumulator.

The flow passage or channel is arranged so that liquid refrigerant is conducted back and forth across the evaporator to render all portions of the adjacent surface effective in absorbing heat. The channel thereafter conveys the refrigerant gas, formed through heat absorption, back along a path lying closely adjacent to the original path. In this way, all portions of the evaporator surface are closely adjacent to the liquid refrigerant portion of the channel, which may be termed for convenience the primary stage, as are also the portions of the return channel, termed the secondary stage, which convey the refrigerant gas.

As will be fully described later in this specification, the

secondary stage of the channel constitutes an accumulator which may be filled with liquid refrigerant to a greater or l' lesser extent depending upon ambient temperature condia tions. -To the extent that the secondary stage does carry Y liquid refrigerant, it aids in absorbing heat and increases the refrigerating capacity of the evaporator.

In view of the close proximity of the secondary Astage to the primary stage, the gas in the secondary stage is maintained at a relatively low temperature and is` relatively dense; consequently, the storage capacity of the f secondary stage for liquid refrigerant is correspondingly increased. i

Although the principles and structure of this inventionif Freezing Apparatus. These patents, however, do not relate to combined evaporators and accumulators as set forth in this application.

p Patented Mar. `2s', 195s Further, because of the limitations iin- Y. tuallyrleavingY by the outlet- Y jthroughV Vthe channel, theY liquid refrigerant absorbs heat and vaporizes into a gas. Under'ordinary operating conbroad object of the invention is the provision of an irnproved evaporator, and more specically an evaporator of extremely simple construction including an accumulator comprising a part of and integrally formed with the main y evaporator passages. Y

kAnother object of the invention isthe provision of an "In view of the foregoing, it will be understood that a Y tion.

evaporator having a continuous ow channel, portions of Y,

which 4,are intercalate'd to define a storage volume which mayserve as an accumulator. K

A further advantage of theinvention is the provision ofV an evaporator which during operation has a relatively A uniform surface temperature andis free from dead areas s Ywhich do not contribute to useful refrigerating capacity.Y

of operating thenovel evaporator whereby'uniform absorption of heat by the entire ,evaporator is attained with a refrigerating eci'ency proportional to the demand irnposed onthe evaporator. Y

AIt is also Van object of the invention Vto, provide. a method 1A, still further advantage ofthe invention ispthat itV yields an eicient evaporator which can be very easily fabricated at low cost for use in a refrigeration'system. The novely features that I consider characteristic of my invention fare set forth in the appended claims; theV invention itself, however, both as` to its organization and Vuse, together with additional objects and advantages thereof, will best be understood from the following description of specile embodiments when read in conjunction with' the accompanying drawings, in which:

Y Fig. l is a plan view of rollabonded sheets having a dowV channel arranged according tothe principles ofithe inan evaporator;

Fig. 2 is an edge View of the roll bonded sheets shown inFigl;

Eig. 3 isa cross sectional view taken on plane 3 3V of'Fig.V l showing the flow channel in cross section; Fig. 4 `is a plan View jof roll bonded sheets comparable to those shown in Fig.V l but having .a different pattern yofow channels illustrating a modified version of the Y invention; f

Fig. 5 is an edgerview of the structure shown in Fig. 4; Fig. 6 isaY cross sectionalview of primary and secondaryow passes proportioned in accordancewith another modification of the invention;

Fig.'7ris also a plan View of ing still anothermodiication of the'iiow channels embodying the .principles of the invention; j

roll bonded sheets show- Y vention, the presence of refrigerant in the ow cllannelV Ybeing shown diagrammatically. Thefigure shows the sheets as they appear in the flat prior to formation into flows through theevaporator outlet back include a continuous channel 6 which conveys refrigerant from inlet 7 to outlet 8. The roll bonded sheets 1 and 5 of the respective Figs. l and 4 are arranged Vto be bent into an evaporator such as illustrated in Fig.V l). This type of evaporator is commonly termed a front-toback wrap evaporator and in vertical section has a C'.Y forma- It` is commonly positioned at the top of a'refrigerator cabinet in position toV receive food to beV Vstored under low temperature conditionsV within volume 9. The

inlet and outlet of the refrigerant flow channel arerporsitioned at one side of the linished evaporator as illustrated the left. to Vthe right within the refrigerator. A rear wall l5 made of sheet metal aids Vin'en'closing the vfood storage space denedby the evaporator. The' inlet and outlet VconnectionsV are locatedat the rear of the evaporator as indicated at-16; Y Y Y, K

In Figs. l, 4, and 7, phantom linesindicate bend lines, being the points of Vtangency of the straight sections of the Ainished .evaporators with the radiused Vcorners as Y shown in Figs. 9 and`l0.V

ltwill .be understood by those skilledin the art that evap'oratorsY of vthe Ytype illustrated comprise one component. of a Vclosed refrigerant system. Vrnonly used system, a compressor is provided which compressesga'seous refrigerant and delivers it to a condenser Vwhere heat is extracted from the gas and it lundergoes a Y change of state, returning to liquid form. The liquid f refrigerant isr then .passed through a pressure reducing means, such as a capillary tube, fromwhich the low pressure refrigerant, liquid ows to the inlet of the evapora-` Here heat absorption causes the liquid refrigerant tor. to Vreturn tothe gaseous state. VThis refrigerant gas then to the compressor forarepetitionY ofA this cycle of operation. Obviously,

' driers and lter's may be provided in the system to remove Vwater and other impurities which would hinder'its proper operation.` 'i

Returningto aconsideration of Pig. Yl, Vit will be observed that now, channel 2 extends frominlet 3 around Fig. V8 is'an edge view of the structure shown in Fig. 7;

Fig. Y9 isa rear elevational view of an evaporator formed Y' frornthe roll bonded sheets shown in Eig. 7, a part of the rear'wall being broken away to simplify the illustration; and` Y f Y Y Fig. l0 is'a rside elevational view of' an evaporator VYformed from sheetsl of the typeshownin Figs, l and 4 with the side wall partially brokenY awayY to simplifythe illustration.

Before YconsideringV the functional advantages of the invention, it is welli to Yunderstandthe structuresset forth.

Directing attention first to Fig'. l, it will Ybe notedl that roll'bonded sheets, Vgenerallydesignated), Yare formed to define a continuous refrigerant flow channel Zierxtend.-

ing between an inletV 3 and an `outlet '4 located at oneV yedge of the'sheets. Liquid Yrefrigerant is introduced toV the Vperiplneryjof sheetsl, asindicated at 17. At 18 the channel departs-from theperiphery ofthe sheets and Vextends, Yfrornfright to` left sinuously `defining a plurality of parallel passes 19..V Adjacent parallel passes are ,ioined at `opposite ends by return bends 20,and,21.

Invthis manner the; refrigerant introducedas a liquid at VY3 passes through the` channel lndeventually arrives at.k vpoin t',22. d The channel frorninlet 3 to'point 22 is knownY as thefprimary Astagey At 2,2,the refrigerant enters another series of parallel passes 23:j,oined atgtheir ends by return bendsVV 24 and 25.-k The lastparallel pass, indicated" at 26 is' directly connected to outletr4. Y

Theportion of the channel. from point 22 to'outlet 4 is .termed'thefsecondary*stagef of the evaporator.Y

. Attention Vrnaynow be directed to Fig.,l3sho'wing' theV Y 'cross sectional shape ofthe channel in the. primary stage the inlet in Vany conventional manner, as YbyV a capillary'ir Y tube (not shown) Yandilows through the channelY 2 even- In the course of its travei ditions only refrigerant gas leaves by outlet 4.

' Y Directing attentionnow to Fig. 4it will be noted that similar rollebonded sheets are indicated' 'atq Y.ar-id ag'ain andY in the secondary stage.

noted 'that the V-passesfltwe Vflattened topY and' bottom walls 27; and 2,8 formed by engagement of the roll Vbonded sheets with 1the platens during the inflation process, as has been described,V i Y. i Y Attention `is now specifically.,directedY to the yarrange-k ment of'pa'rallel .passes 19.and"23.i Itwill be observed."

that the passes 23, whicharepart of the secondary strage,

Ylie closely-adjacentft and betweenparallelk passes 19 1V In the most com- -Y Y In .thisl Vfigure the periph- Y erallpass- 17 is. shown'to the left'and return bendZS iof thesecondaryj stage is shownV to .the right; it will be which comprise part of the primary stage. YThis interspersed arrangement has been termed intercalation During use, liquid refrigerant introduced at 3 passes through the primary stage Where it absorbs heat and gradually vaporizes. ln the course of doing so, the refrigerant flows through passes i7 and 19 and, in this Way, is enabled to absorb heat from substantially the entire surface of the evaporator prior to arriving at point 22 Where the mixture of liquid and gaseous refrigerant enters the secondary stage. The refrigerant then flows through the parallel passes 23 of the secondary stage Where sucient additional heat is absorbed to change the refrigerant completely into gas prior to leaving the evaporator and outlet To the extent that evaporation occurs in the secondary stage, the secondary stage contributes to the refrigerating capacity of the evaporator.

The amount of liquid refrigerant present in an evaporator at any time depends upon the temperature of the air surrounding the refrigerator and the heat load on the evaporator. To illustrate, when a refrigerator is operated in a region of low temperature, the condenser readily dissipates heat which favors rapid condensation at low pressure and results in backing-up or dammingup a sizable portion of the refrigerant in liquid form in the condenser. The relatively low condenser temperature also results in a relatively low discharge pressure from the compressor and consequently in a low pressure dierential across the capillary tube which conveys liquid refrigerant to the evaporator. Under such conditions, only a portion of the total refrigerant charge is present in the evaporator as liquid. At such time, the secondary stage of the evaporator runs substantially dry, i. e., is filled with refrigerant gas rather than liquid. It will be appreciated that little or no accumulator capacity is necessary under such conditions.

The need for an accumulator will be understood from a review of conditions prevailing when the refrigerator operates in a region of high ambient temperature. The higher condenser temperatures then prevailing result in higher condenser pressure and less damming of liquid refrigerant in the condenser. As a result, an increased pressure differential exists across the capillary tube supplying the evaporator, and an increased portion of the liquid refrigerant is present Iin the evaporator. Under such operating conditions, an accumulator is necessary to accommodate the increased amount of liquid and, in the present invention, the passes of the secondary stage are partially or totally filled with liquid refrigerant to the extent required. The secondary stage then functions much as the primary stage and contributes to the refrigerating capacity of the evaporator. The importance of this feature will be appreciated when it is recognized that evaporator capacity increases with ambient temperature and compensates for the correspondingly greater heat leak into the refrigerator then prevailinff.

From an ideal design standpoint, the primary stage should be made just large enough to have sumcient heat absorbing capacity for the needs of the refrigerator when operating at the lov/est ambient temperature to be encountered. Since the increase in the amount of liquid refrigerant present in the evaporator is related to ambient temperature rise, it will be appreciated that the extremes of ambient temperature conditions between which satisfactory operation is possible is a function of the accumulator capacity. The extremes for which domestic refrigerators are normally designed are 50-ll0 F. For this reason, it is desirable to provide large accumulator capacity, which may be effectively accomplished by the present invention.

The accumulator also compensates for variations in the amount of refrigerant with which the system is initially charged. A large accumulator lsimplies charging by providing increased charge tolerance.

Returning to a consideration of Fig. l, it will be noted that the primary and secondary stages, being intercalated,

asoma/.1.

leave no areas of the evaporator which might operate at an elevated temperature. Instead, low temperatures generally prevail through the evaporator and, in fact, the primary stage tends to lower the temperature of the secondary stage and the gas therein, thereby increasing its liquid storage capacity.

As suggested earlier in the specication, dead areas of relatively high temperature are very objectionable in an evaporator since the frost, which normally accumulates on an evaporator, may tend to melt in the dead areas.

The ow channel of 1iig. l has been cross hatched to indicate the disposition of refrigerant under typical operating conditions between the extreme ambient temperatures for which the refrigerator is designed. It will be understood that the refrigerant, which enters as a liquid at 3, gradually vaporizes as it absorbs heat in the primary stage. The gas and liquid mixture has been indicated by double cross hatch lines.

Since a portion of the secondary stage must function as an accumulator at any ambient temperature above the minimum design temperature, the liquid and gas mixture has been shown filling the secondary stage to point A. The remainder of the secondary stage is lled With-refrigerant gas maintained at low temperature by the adjacent primary stage, as has been explained.

The function of the primary and secondary stages is the same regardless of the disposition of the sheets, either as shown in Fig. l or as in Fig. lO.

The refrigerant and integral evaporator and accumulator constitute a novel combination embodying the principles of the invention. The disposition of the refrigerant at ambient temperatures above the minimum is substantially the same in the structures shown in Pigs. 4 and 7 as indicated in Fig. l, i. e., a portion of the mixture of refrigerant gas and liquid will be present in the secondary stage, and the primary stage will be full as indicated.

The configuration of the flow channel shown in Fig. 4 embodies somewhat the same principles as in Fig. l. lt will be noted, however that the primary stage extends from inlet 7 to point 29 Where the refrigerant gas and liquid enters the secondary stage. The secondary stage extends from point 29 to outlet 8.

The parallel passes 3d and 3l of the primary and secondary stages, respectively, are again intere-elated as has been described in connection with Fig. l. it should be observed, however, that additional passes 32, 53, and 34 have been provided conveying the refrigerant from the parallel passes; to the outlet i3. These additional passes again are located quite close to portions of the primary stage to assure temperature uniformity and maximum effectiveness of the secondary stage in acting as an accumulator.

To increase the refrigerating capacity of the primary stage, parallel flow passes may be provided as at 35 and 36. The primary stage may reverse in direction, as at 37, to avoid mechanical fasteners Which extend through holes 3S in connection with the attachment of defrosterheaters and controls.

A plurality of holes 35i may be formed adjacent each side edge of the sbee to accommodate rivets used for securing end panels to the evaporator after it is formed to the shape shown in l0.

in 7, the primary stage extends from inlet 13 to point di?. The secondary stage extends from point 40 to outlet 14.

It will be noted that brancher passes ii-46 have been provided in the primary stage to increase the refrigeratng capacity of the structure, particularly near the edges Where heat transfer is greatest. T he primary stage also includes a plurality of parallel passes 57 which are intercalated with parallel passes of the secondary stage.

It Will be noted that the inlet i3 and outlet l of the structure sho-wn in Fig.v are relatively remote when the Y isfin the flat.

the .configuration shown in Fig. 9,y the: inlet andlfoutlet are brought close together to facilitate yeonnectionVY in the closed refrigerant system which has been; described. f A series of holes 49 may be'proyided along one'redge Y to facilitate attachment of the rear yvall, The left'and which are bonded together.

Y illustrated made from 2S() aluminum, the wallthickness Vright endsrof the sheet are also provided with holes 50 to permit riveting, as illustrated atl51 in Fig-.9.

From what has been said, it Will be understoodthat it Yis desirable to provide as` large an accumulator, fand hence a secondary stage, as possible.y Although for many applications itis desirable to make thev secondary stage safran ttresheet is formed intoy oneV dow channel may be devoted to Vthe primary stage low secondary stage temperatures maybe attained, and.`

Vlarger than the primary stage, it is recognized that for some usage the Vsecondary stage may actually hev smaller. 'Ifo illustrate,rin Fig. l the ratio by volumeof the primary to the secondaryl stage is in the order of 60;4.0.

`11 the structure shov'vnY in Fig.l4v the primary and secondary stages haveY equal length and the passesi have Y cross sections of equal area.,V As, a result, theprimary and secondary stages have substantially identical internal volumes.

Y In the structureshown in Figi.' 7, the volume ratio of the primary stage to the secondary stage is in the order,

be used in a rollV bonded evaporatoris a function of operating pressure, as well as thickness of the sheets In evaporators of the `type ofthe passes as finally formed is approximately .O30 inch and the evaporatormust withstand test pressures of 350p. s.V i. g. For .these parameters, maximum cross sectional width Yof the flow 'channel is approximately 1%2 of an inch. As a practical matter, it is desirable to.

' provide owrpaths of this maximum width in both the primary and secondaryY stages. Por this'reason, increased capacity of thesecondary stage is usually accomplished than in the' primary stage.

by providing increased length of tlov'v channel in the secondary stage. Y Y Y,

YIn other processes, however, where no dimensional 11mi- "tation is imposed, it is desirable to make thecross sec- The cross sectional width of the jow channel that may tional area of the passesin the secondary stage larger Arsimilar relationship of'ow areasvmayrbe utilized Y in roll bondedevaporatorsrifthe thickness `of the sheets Vare appropriately increased. Although this is possible, Y

l,it is VVfrequently not desirable Abecause of Ythe increased i 'cost Vresultingfrom use ofthicker material and different alloys.

Thus, control of accumulatorvolume in the secondary I V stage isafunctionof channellength as well as `channel cross section. Either length of cross sectional'area or bothniay be varied as desired to provide a large secondai-y stage withr'ampleaccumulator capacity Yto meet the requirements of the refrigerator.

The left-to-righ't'type evaporator lends itself particularly wellito Vapplication of this invention. This stylefof evap- VoratorQhas Vmore surface area, and hence can. accommo- Y date a longer refrigerant channel, than fa frfrovnt-to-back` evaporator.Y Since only a certainsizeV primaryL stageis required for given refrigerationrequirements, the additional refrigerant channel may be devoted toV accumulator volume.

, ARecently there has been madeavailable to vthe industry faprocess for roll bonding several layers of sheets to-A Y. gether simultaneously.' ln this way, yfor example,V three "sheetsof material may be :joined simultaneously to proa Y Yidetw series Vof ow channels which, although they more efficient than Y capacity.' Y

.3; The method of continuously operating a refrigerator 'perature Y conditionsV Vadecting may be overlapped, are none the less separated by an i n. termediate sheet of material. This type of structure also lends itself Well to the application of this invention sincek andthe other ow channel, on the other side, of the inteormediate sheet, may be devoted to the secondaryl stage. The resulting operation will be essentially theV same, since the principlesof uniform temperature distribution Yand a large accumulator volume may be provided in the secondary stage without theV use of aV separate accumulator.v

ln view of the foregoing, it will be appreciated by those skilled in the art that through thisinvention an evaporator of improved eiciency andV refrigerating capacity has been provided. The need for a separate accumulatorfis eliminatedand the refrigerant ilow channel itselfis used for thisrpurpose. The refrigerant liquidthat may be present iu Vthe accumulator aids in absorbing heat in a manner far accumulators. 'e Y vThe various features and advantages of the design and construction disclosed are thought to be clear from theV foregoing description. 'Various V'other features and ad-Y Vvantages, not speciiically enumerated Vwill undoubtedly ocCur'to those yersed in the art, as likewise willmany variations and modifications of the preferred embodiments of the inventionY illustrated, all of which may be achieved without departing from the spirit and scopeV ofV the invention. o Y

Having described a preferred embodiment of myinvem tion, 1 claim;

l. `The method of operating a refrigerator evaporatork formedl Yfrom a Vrigid metallic sheetarid a continuous flow channel for conveying liquid and gaseous refrigerant,V the iirst portion of which Vchannel is positioned to absorb heat from the entirerarea of the sheet and the secon-d portion of which isdisposed in heat'trans'fer rela-V tionship with the first portion comprising maintaining the first portion'of the channel full of liquid and gaseous refrigerant mixtureat alltimes, lling the second portion of `the channelwith such mixture onlyjto an extentV propoi-tional to the 'rate of heat absorption required Vof the evaporator, and iilling theremainderof the second por-'-V V45' tion with refrigerant gas, whereby theV entire area of theV evaporator is effective in absorbing heat at all Vtimes and VtheY refrigeratingY capacity of the evaporator lis adjusted as required'to meet pret/,ailing demandsfor refrigerating capacity. 2. Themethod ofV continuouslyv operating a refrigerator evaporator having a metallic sheet With Ywhich a re-V Y frigerant channelY is associated ink heat transfer: relationship, the channel including'a first'portion for absorbing heat from substantiallyY the entire areal of the sheet and "a second portion in heat transferA relationshipwith the iirstV portion comprising maintainingY liquid Vrefrigerantirr Y the `first portion at all times and maintaining liquid refrigp erant in the second portion'fonly vto an extent commen-V` requirements forY refrigerating surate; with Yprevailing evaporator having a sheet withwhich a 'refrigerantrchan nel Vis associated in heat ,transfer relationship, thev channel including a lfirst portion forY absorbing heat fromsubstan- Y tially thejenti're area of the sheet and a second portion in heat transfer relationship .with the first portion Ycomo prisingmaintaining 'liquid' refrigerantin Vthe Vfirst portion at all times and maintaining liquid refrigerant `in the second'portion to Yan extent proportional to ambient temthe evaporator is located. Y Y

.4, The method of producing refrigeration by .use ofan Y evaporator including aV conduit forconveying'refrigerant in liquid and gaseous` form comprising passing liquid refrg- ,7 erantfthrough `a first portion of the conduit inheatex- 5 Y change relationship vWith substantiallythe entirearea of possible with' 'conventional'V the refrigerator in'whichy said evaporator, and then passing liquid refrigerant and gaseous refrigerant formed during said first step through a second portion of the conduit in heat exchange relationship with the rst portion.

5. The method of producing refrigeration comprising conveying liquid refrigerant into heat absorbing relationship with a surface to be refrigerated and then conveying refrigerant gas resulting from absorption of heat from the surface and any remaining refrigerant liquid into inti- References Cited in the le of this patent mate heat transfer relationship with portions of the refrig- 10 2,712,736

erated surface.

UNITED STATES PATENTS Davenport May 13, 1930 Heath June 6, 1939 Benson Mar. 13, 1945 Philipp Feb. 7, 195o Philipp Dec. 2, 1952 Wurtz July 12, 1955 

